| 1 | M & M Investments | | Oil & Gas Operator | May 1990 |
| 2 | M-P Petroleum, Inc. | McPherson, KS 67460 | Oil & Gas Operator | Jan 2013 |
| 3 | M. F. McCain, Inc. | | Oil & Gas Operator | Jul 1987 |
| 4 | Mack Energy Co. | Duncan, OK 73534 | Oil & Gas Operator | Dec 2025 |
| 5 | Magnum Hunter Resources Corporation | | Oil & Gas Operator | Nov 2019 |
| 6 | Manti Exploration Operating LLC | Corpus Chrsti, TX 78403 | Oil & Gas Operator | Feb 2015 |
| 7 | Manti Operating Company | Covington, LA 70435 | Oil & Gas Operator | Feb 2026 |
| 8 | Mar-Low Corporation | | Oil & Gas Operator | Mar 1992 |
| 9 | Marathon Oil Company | Houston, TX 77252 | Oil & Gas Operator | Dec 2025 |
| 10 | Mariner Energy, Inc. | Houston, TX 77042 | Oil & Gas Operator | Nov 2010 |
| 11 | Marquee Corporation | Houston, TX 77024 | Oil & Gas Operator | Feb 2026 |
| 12 | Marquis Resources, LLC | | Oil & Gas Operator | Jul 2021 |
| 13 | Marsh Engineering, Inc. | | Oil & Gas Operator | Dec 1990 |
| 14 | Masters Resources, L.L.C. | Houston, TX 77079 | Oil & Gas Operator | Dec 2008 |
| 15 | Matzinger & Bell Inc-Carl O&G | | Oil & Gas Operator | Dec 1981 |
| 16 | Matzinger & Bell, Inc. | | Oil & Gas Operator | Dec 1982 |
| 17 | Matzinger Petroleum Co. | | Oil & Gas Operator | Jan 1991 |
| 18 | Maximum Energy, Inc. | | Oil & Gas Operator | Aug 2001 |
| 19 | Maxus Exploration Company | Dallas, TX 75201 | Oil & Gas Operator | Jan 1995 |
| 20 | McAlester Fuel Co. | Houston, TX 77042 | Oil & Gas Operator | Jan 2010 |
| 21 | McCormick Operating Company | | Oil & Gas Operator | Mar 1984 |
| 22 | McCormick Operating PRTNSHP | | Oil & Gas Operator | Sep 1985 |
| 23 | McCormick-Ciroco, Inc. | | Oil & Gas Operator | Jan 1984 |
| 24 | McLain J. Forman | | Oil & Gas Operator | Mar 1988 |
| 25 | McMoran Oil & Gas LLC | New Orleans, LA 70160 | Oil & Gas Operator | Oct 2021 |
| 26 | McOr Oil Development, Inc. | | Oil & Gas Operator | Feb 1990 |
| 27 | McRae Exploration, Inc. | | Oil & Gas Operator | Mar 1984 |
| 28 | McRae Oil Corporation | | Oil & Gas Operator | Mar 1984 |
| 29 | MCZ, Inc. | Houston, TX 77026 | Oil & Gas Operator | Sep 1990 |
| 30 | Meridian Oil Inc. | Houston, TX 77210 | Oil & Gas Operator | Aug 1996 |
| 31 | Meridian Oil Offshore Inc. | | Oil & Gas Operator | Aug 1996 |
| 32 | Merit Energy Company | Dallas, TX 75240 | Oil & Gas Operator | Feb 2026 |
| 33 | Merrico Resources, Inc. | Ardmore, OK 73402 | Oil & Gas Operator | Mar 2008 |
| 34 | Michel T. Halbouty | | Oil & Gas Operator | Dec 1996 |
| 35 | Michigan-Wisconsin Pipe Line Co | | Oil & Gas Operator | Dec 1983 |
| 36 | Mideast Gas Systems, Inc. | Midland, TX 79702 | Oil & Gas Operator | Dec 2005 |
| 37 | Milagro Exploration, LLC | Houston, TX 77010 | Oil & Gas Operator | Aug 2018 |
| 38 | Mission Resources Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2008 |
| 39 | Mississippi Ventures | | Gas Operator | Feb 1992 |
| 40 | Mobil E&P North America Inc. | | Oil & Gas Operator | Jan 1994 |
| 41 | Mobil Oil E & P Southeast Inc | | Oil & Gas Operator | Sep 2013 |
| 42 | Moore McCormack Energy, Inc. | | Oil & Gas Operator | Jul 1988 |
| 43 | Mosbacher Energy Company | Houston, TX 77002 | Oil & Gas Operator | Feb 2026 |
| 44 | Mullins & Prichard | | Oil & Gas Operator | May 1992 |
| 45 | Murphy Exploration & Prod. Co. | Houston, TX 77094 | Oil & Gas Operator | Jun 2011 |
| 46 | MW Petroleum Corporation | Houston, TX 77056 | Oil & Gas Operator | Mar 2015 |